lol
I don't have any personal experience with these "plush puppies" so I couldn't tell you for sure. I can only tell you what I've read...and ,in terms of being "reef safe", the opinions given by the experts and the hobbyists seem to contradict one another.
I think the crab would be exhibiting whatever behavior it is showing in a larger tank as well...but the aggression would be less noticeable because you wouldn't see it as often and the fish/inverts would have more space to avoid the crab.
In general, most crabs are opportunistic feeders and will catch what they can. But if you feed the crab you MAY notice that its potential for attacking something you like will decrease.